1. Field of the Invention
The present invention relates to a fluorene-based compound and an organo-electroluminescent device using the same. In particular, the invention relates to a fluorene-based compound comprising a fluorene or a spirofluorene structure at both terminals, and a spacer including one or more atoms between the terminal fluorene or spirofluorene structures. The invention is further directed to an organo-electroluminescent device having an increased internal and external light emitting efficiency and improved color purity by forming high quality organic layers through dry and wet processes using the fluorene-based compound.
2. Description of the Related Art
Organo-electroluminescent devices are active light emitting display devices that emit light by recombination of electrons and holes in a thin layer made of a fluorescent or phosphorescent compound (an organic layer) when a current is applied to the organic layer. The organo-electroluminescent devices have various advantages, such as being lightweight, having simple constitutional elements, and having a simple fabrication process, while providing a superior image quality and wide viewing angle. Furthermore, the organo-electroluminescent devices can create nearly perfect dynamic images having high color purity. The organo-electroluminescent devices also have electrical properties making them suitable for use in portable electronic equipment, such as low power consumption and low driving voltage.
Organo-electroluminescent devices are known in the art. For example, a multi-layered organo-electroluminescent device using an aluminum quinolinol complex layer and a triphenylamine derivative layer was developed by Eastman Kodak Co. (U.S. Pat. No. 4,885,211). In another example, a wide range of light from ultraviolet light to infrared light can be emitted using low-molecular weight organo-electroluminescent materials (U.S. Pat. No. 5,151,629).
Light emitting devices, which are self-illuminated light emitting display devices in contrast to backlit displays with an independent light source, have wide viewing angles, excellent contrast and quick response. Such light emitting devices can be classified into inorganic light emitting devices using inorganic compounds to form emitting layers and organic light emitting devices (“OLED”) using organic compounds to form emitting layers. Organic light emitting devices are brighter, have lower driving voltages and quicker responses than inorganic light emitting devices. Furthermore, organic light emitting devices can realize multiple colors. For these reasons, organic light emitting devices are being actively studied.
Conventionally, an OLED has a layered or laminated structure. For example, a typical OLED has an anode/organic emitting layer/cathode multilayered structure. An OLED can also have various other structures, such as an anode/hole injection layer/hole transport layer/emitting layer/electron transport layer/electron injection layer/cathode multilayered structure or an anode/hole injection layer/hole transport layer/emitting layer/hole blocking layer/electron transport layer/electron injection layer/cathode multilayered structure.
Materials that are used in organic light emitting devices can be classified into vacuum deposited materials and solution coated materials according to a method of preparing an organic layer. The vacuum deposited materials may have a vapor pressure of greater than or equal to about 10−6 torr, at a temperature of 500° C. or less and are low molecular materials having a molecular weight of 1,200 g/mol or less. The solution coated materials may be highly soluble in solvents which are prepared in a solution phase. Solution coated materials can include aromatic or heterocyclic groups.
When the vacuum deposition is used to prepare an organo-electroluminescent device, the manufacturing costs are increased due to the cost of using a vacuum system. In addition, when a shadow mask is used to prepare pixels to display natural colors, pixels having high resolution are not readily produced.
On the other hand, solution coatings can be formed readily by spin coating or by printing, such as by inkjet printing and screen printing. Accordingly, organo-electroluminescent devices can be fabricated using solution coatings in a simplified manner and at a lower cost. Using the solution coatings, relatively high quality resolution can be obtained compared to the shadow mask.
However, materials that are used in solution coatings can have lower thermal stability which can result in e.g., lower color purity, and other compromised properties than would those deposited by vacuum deposition methods. In addition, the materials used in solution coatings can be crystallized and to provide the resulting particle size from wavelength of visible lights. In this way, a white residue may occur by scattering of the visible light or from the formation of pin holes in the coating, thereby degrading properties of the organic light emitting devices, even though the materials have excellent properties in thermal stability and color purity.
Japanese Patent Publication No. 1999-003782 discloses an anthracene substituted with two naphtyl groups, which can be used as a light emitting layer or a hole injection layer. However, the substituted anthracene is not sufficiently soluble in solvents, and properties of an OLED using the same are unsatisfactory.
Conventional OLED devices thus continue to have several problems including high drive voltage, low color purity and low emission efficiency. Therefore, there remains a need to develop an OLED having properties such as low driving voltage, excellent brightness, light emitting efficiency and color purity using a light emitting compound which has excellent thermal stability and is capable of forming an excellent organic layer formed using a solution coating method.